Reaction times of pigeons on a wavelength discrimination task

After extensive pretraining, three pigeons were exposed in 2-second trials to a random series of 14 light wavelengths, ranging in one nanometer (nm) steps from 575 nanometers to 589 nanometers. Responses to one of the wavelengths, 582 nanometers, were intermittently reinforced. The relative frequency of response approached 1.0 at 582 nanometers, and decreased with progressively higher and lower wavelengths. Reaction times shorter than about 0.2 second occurred with a low frequency that was largely independent of wavelength. Wavelength controlled the frequency of longer reaction times, but did not affect the distribution of these reaction times. Consequently, receiver-operating characteristic curves constructed by using reaction time as a rating measure did not conform to the signal-detection model, in contrast to such conformity when response rate is used in a similar way. The data suggest that stimulus onset as such triggers early response emission with some small probability; the probability of responses with longer latency is controlled by wavelength, but their time of emission is controlled by some independent process.     

Stability criteria

Three approaches to the determination of behavioral stability were examined. In the first, a learning curve was fit to acquisition data (from Cumming and Schoenfeld, 1960), and the “experiment” stopped when the data approached sufficiently close to the theoretical asymptote. In the second, the data were analyzed for variability and linear and quadratic trend. In the third, the experiment was stopped when the magnitude of the daily changes in the data fell below a criterion. Accuracy was measured as deviation between the average value of the dependent variable when the experiment was stopped, and the average value over the last 100 sessions. The first approach was most accurate, but at the cost of requiring the most sessions and being the most difficult to apply. Both the second and third approaches provided acceptable criteria with a reasonable cost-accuracy tradeoff. The second approach permits a continuous adjustment of the criteria to accommodate the variability intrinsic in the experimental paradigm. The third, nomothetic, approach also takes into account the decreasing marginal utility of extended training sessions.     

Drug discrimination under concurrent variable-ratio variable-ratio schedules

Pigeons were trained to discriminate 5 mg/kg pentobarbital from saline under concurrent variable-ratio (VR) VR schedules, in which responses on the pentobarbital-biased lever were reinforced under the VR schedule with the smaller response requirements when pentobarbital was given before the session, and responses on the saline-biased key were reinforced under the VR schedule with the larger response requirements. When saline was administered before the session, the reinforcement contingencies associated with the two response keys were reversed. When responding stabilized under concurrent VR 20 VR 30, concurrent VR 10 VR 40, or concurrent VR 5 VR 50 schedules, pigeons responded almost exclusively on the key on which fewer responses were required to produce the reinforcer. When other doses of pentobarbital and other drugs were substituted for the training dose, low doses of all drugs produced responding on the saline-biased key. Higher doses of pentobarbital and chlordiazepoxide produced responding only on the pentobarbital-biased key, whereas higher doses of ethanol and phencyclidine produced responding only on this key less often. d-Amphetamine produced responding primarily on the saline-biased key. When drugs generalized to pentobarbital, the shape of the generalization curve under concurrent VR VR schedules was more often graded than quantal in shape. Thus, drug discrimination can be established under concurrent VR VR schedules, but the shapes of drug-discrimination dose-response curves under concurrent VR VR schedules more closely resemble those seen under interval schedules than those seen under fixed-ratio schedules. Graded dose-response curves under concurrent VR VR schedules may relate to probability matching and difficulty in discriminating differences in reinforcement frequency.     

Remembering,forgetting and (dis)enfranchised grief in everyday settings in English and Welsh towns: Migrants' and minorities’ translocal and local memories associated with funerary spaces and practices

In this paper we explore migrants' and minorities' memories and memory-making associated with death, funerary and remembrance practices, with particular attention to how this intersects with experiences of migration and/or being part of a cultural or religious minority. The paper examines different spaces including bodies, homes, translocal networks, cemeteries and crematoria, centred on insights from focus groups, biographical and key participant interviews in four medium sized multicultural towns in England and Wales. These case studies afford an exploration of the complex and dynamic ‘ecologies’ of migrant and minority memories and sense of citizenship in relation to death, bereavement and remembrance spaces and practices. Participant accounts highlight memories of past practices, (post)colonial marginalization, disenfranchisement, changes in practices, the strains of transnational grieving, pragmatic compromises and collaborating to improve funerary provision as endeavours of everyday citizenship. These are explored through two broad interlinked themes: firstly, translocal memories of past and evolving funerary and remembrance spaces, customs and practices; and secondly, relationality and autonomy through the choice of where to situate the dead, and implications for associated future memory-making.     

Dissociating the two faces of selective memory retrieval

Research in the past four decades has repeatedly shown that selective retrieval of some (non-target) memories can impair subsequent retrieval of other (target) information, a finding known as retrieval-induced forgetting. More recently, however, there is evidence that selective retrieval can both impair and enhance recall of related memories (K-H. T. Bäuml & Samenieh, 2010). To identify possible experimental dissociations between the detrimental and the beneficial effects of memory retrieval, we examined retrieval dynamics in listwise directed forgetting, varying the delay between preceding non-target and subsequent target recall. When target recall immediately followed non-target recall, we replicated the prior work and found detrimental effects of memory retrieval on to-be-remembered items but beneficial effects on to-be-forgotten items. In contrast, when a delay was introduced between non-target and target recall, the detrimental effects were present but the beneficial effects were absent. The results demonstrate a first experimental dissociation between the two effects of memory retrieval. They are consistent with a recent two-factor account of the two faces of selective memory retrieval.     

Retrieval-induced forgetting after trauma: A study with victims of sexual assault

The Retrieval-Induced Forgetting (RIF) paradigm is used to study how the repeated retrieval practice of particular memories impairs the retrieval of related memory traces. A study is reported where this automatic form of forgetting was investigated in a group of sexual-assault victims and a control group. Using a recognition-cued RIF task, the present study examined RIF with neutral, positive, negative and trauma-specific stimuli. Response time data showed that irrespective of previous trauma exposure, a RIF effect was observed for neutral material, but not for emotional material. No differences in RIF between the trauma group and the control group were found. Inconsistencies with previous literature and the implications for emotional memory are discussed.     

Lorenz Curves: A New Model for the Distribution of Psychiatric Services

The growth of child and adolescent psychiatric services based on the wraparound philosophy raises new questions for medical directors, investigators, and clinicians interested in improving quality of care and outcomes. Typically, quality improvement studies have focused on standardizing care and decreasing variation while community based services following a wraparound model are by definition individualized. To date, little information on how to evaluate such services in a managed care environment has been available. We present one option for evaluating the distribution of medical services and the extent to which providers individualize services for children with severe emotional disorders. Specifically, we (a) review the philosophy and goals of wraparound services, (b) introduce the Lorenz curve as a tool for determining the degree of inequality in service distribution at a given institution, and (c) present a case study on the use of Lorenz curves by a Medicaid Behavioral Health Organization in profiling behavioral providers.     

Make‐or‐Break: Chasing Risky Goals or Settling for Safe Rewards?

Humans regularly pursue activities characterized by dramatic success or failure outcomes where, critically, the chances of success depend on the time invested working toward it. How should people allocate time between such make‐or‐break challenges and safe alternatives, where rewards are more predictable (e.g., linear) functions of performance? We present a formal framework for studying time allocation between these two types of activities, and we explore optimal behavior in both one‐shot and dynamic versions of the problem. In the one‐shot version, we illustrate striking discontinuities in the optimal time allocation policy as we gradually change the parameters of the decision‐making problem. In the dynamic version, we formulate the optimal strategy—defined by a giving‐up threshold—which adaptively dictates when people should stop pursuing the make‐or‐break goal. We then show that this strategy is computationally inaccessible for humans, and we explore boundedly rational alternatives. We compare the performance of the optimal model against (a) a myopic giving‐up threshold that is easier to compute, and even simpler heuristic strategies that either (b) only decide whether or not to start pursuing the goal and never give up or (c) consider giving up at a fixed number of control points. Comparing strategies across environments, we investigate the cost and behavioral implications of sidestepping the computational burden of full rationality.     

Determinants of instrumental extinction in terrestrial toads (Bufo arenarum)

Previous research in a water-reinforced instrumental training situation with toads (Bufo arenarum) has shown that performance in both acquisition and extinction is poorer after partial, rather than continuous reinforcement training. In Experiment 1, the performance of a group receiving 24 trials on a 50% partial reinforcement schedule was poorer in acquisition and extinction than that of continuously reinforced groups matched for trials or reinforcements. However, partially reinforced toads extinguished at the same rapid rate as a continuously reinforced group that received training only on the days in which the partial toads received water reinforcement. In Experiment 2, extinction was faster after 10 reinforced acquisition trials than after 30 trials. This evidence suggests that the deleterious effects of partial reinforcement in toads can be explained by a combination of two factors, namely, the distribution of reinforced trials across days and the total number of reinforcements.     

Nonuniform effects of reinstatement within the time window

A time window is a limited period after an event initially occurs in which additional information can be integrated with the memory of that event. It shuts when the memory is forgotten. The time window hypothesis holds that the impact of a manipulation at different points within the time window is nonuniform. In two operant conditioning experiments with 68 3-month-old human infants, we tested the predictive validity of the nonuniformity principle for reinstatement—a partial training trial that forestalls forgetting. After demonstrating that 3-month-olds forget the training task after 5 days (Experiment 1), we presented a reinstatement early (immediately), midway (3 days), or late (5 days) in the time window (Experiment 2). Retention increased exponentially with the reinstatement delay. The surprising magnitude of this result, plus its generality across tasks and species, strongly suggests that the timing of reinstatement differentially affects the outcomes of studies on learning and memory.